Alarm device with means to locate an erroneously activated detector

ABSTRACT

An alarm device for the detection of smoke, fire, and the like having a plurality of detectors connected in parallel and energized by a power supply with the coil of a relay in series with the power supply. Relay contacts are arranged to close when the current through the relay exceeds a predetermined value, said contacts being connected through a resistor and in parallel with the detectors so that when a detector operates, it will cause a current in excess of said predetermined value to flow through the coil closing said contacts which in turn will produce sufficient holding current in the relay to maintain the contacts in a closed condition and at the same time permit the actuated detector to continue to draw current. In this way, a detector erroneously actuated can be easily located.

0 United States Patent 51 3,668,676 Sasaki 1 June 6, 1972 ALARM DEVICE WITH MEANS T0 3,268,881 8/1966 Vasel ..340/228 LOCATE AN ERRONEOUSLY 3,321,755 5/1967 Cooke ..340/267 C AT D DET T 3,343,158 9/1967 Tellerman 340/267 3,475,745 10/1969 White, Jr. ..340/228 [72] Inventor: Koju Sasaki, Tokyo, Japan [73] Assignee: Nittan Company, Limited, Tokyo, Japan Ian-{nary f Caldwell Assistant Exammer-W1lliam M. Wanmsky Filed: y 1970 Attorney-Eugene E. Geoffrey, Jr.

21 A LN 35 31 l 1 pp 0 57 ABSTRACT [30] Foreign Application Priority Data An device for the detection of smoke, fire, and the like having a plurality of detectors connected In parallel and ener- July 1, 1969 Japan ..44/61795 sized by a power supply with the coil f a relay in Series with the power supply. Relay contacts are arranged to close when [52] "340/227 340/228 340/213 R the current through the relay exceeds a predetermined value, [51 II!!- Cl. ..G08b 1.9/00 Said contacts being connected through a resistor and in paral [58] Field of Search ..340/274, 276, 228, 256, 213.1, M with the detectors so that when a detector operates it will 340/237 213 cause a current in excess of said predetermined value to flow through the coil closing said contacts which in turn will [56] Reerences Clted produce sufficient holding current in the relay to maintain the UNITED STATES PATENTS contacts in a closed condition and at the same time permit the actuated detector to continue to draw current. In this way, a 2,994,073 7/1961 Pelovitz ..340/276 detector erroneously actuated can be easily locatei 2,935,730 5/1960 Procter..... ...340/276 3,084,338 4/1963 Mauer et a ..340/276 1 Claim, 2 Drawing Figures ALARM DEVICE WITH NIEANS TO LOCATE AN ERRONEOUSLY ACTIVATED DETECTOR This invention relates to an alarm device and more specifi cally to a novel and improved alarm device for the detection of fire and smoke.

Conventional alarm devices generally utilize a plurality of detectors such as smoke detectors connected in parallel and positioned at various remote locations. In such prior alarm devices should a detector operate erroneously and generate an alarm, the detector is automatically restored to its original state immediately after operation, and it is therefore extremely difficult to determine the specific detector which has produced the erroneous alarm and such erroneous operation can be repeated frequently.

Accordingly, one object of the invention resides in the provision of a novel and improved alarm which is so arranged that should a specific detector operate erroneously, the defective detector can be readily located. This end is attained by the utilization of a relay having a coil connected in series with a power supply which supplies energy to the detectors. Normally open contacts of the relay are connected in series with a normally closed switch and a resistor between the conductors supplying energy to the detectors. Should a detector erroneously operate, the relay contact will close to maintain sufficient holding current through the relay coil and at the same time permit sufficient energy to be applied to the detectors so that an erroneously actuated detector will remain in its actuated condition and thereby permit it to be readily located.

The above and other objects and advantages of the invention will become more apparent from the following description and accompanying drawing forming part of this application.

In the drawings:

FIG. 1 is a circuit diagram illustrating an alarm device in accordance with the prior art; and

FIG. 2 is a circuit diagram illustrating an alarm device in accordance with the invention.

Referring to FIG. 1, the power supply 1 is represented by a battery, and it is connected through the coil 2 of a relay to conductors 3 and 4. A plurality of detectors are connected in parallel between the conductors 3 and 4. When one of the detectors is actuated, its impedance is materially reduced and the increase in current is sensed by the relay coil 2 which in turn generates a suitable alarm. When the current through the relay coil 2 is increased, the contacts 21 associated with the coil and connected between conductors 3 and 4 will close and thereby short-circuit the two conductors so that the relay coil 2 will remain energized and the contacts 21 will remain in the closed position. Under these conditions the voltage applied to the detectors becomes substantially zero and since the detectors include semiconductor elements such as silicon controlled rectifiers, the rectifiers will return to their original nonconductive states when the applied voltage is reduced to zero. Accordingly, if such a detector 5 is actuated erroneously, it will be extremely difficult to locate the faulty detector since the rectifiers automatically return to their nonconductive states upon reduction of the applied voltage to zero. In this connection it will be observed that the contacts 21 are closed when the relay coil 2 in energized and the contacts short-cirthe contacts 21 in a closed position once the contacts have been closed by the operation of the detector 5 which actuates the relay.

With this improved arrangement as shown in FIG. 2 activation of one of the detectors 5 will result in a sufficient reduction in impedance to energize the coil 2 and close the contacts 21. Under these conditions an alarm will be generated and at the same time the contacts 21 will be held in a closed position so that a continuous alarm will be sounded.

' While no difficulty will be encountered in the case of an actual emergency, should a detector be actuated by reason of a fault occurring within the detector, this invention enables the faulty detector to be located. By reason of the use of the resistor 7, the conductors 3 and 4 will not be short-circuited and a sufficient voltage will remain between conductors 3 and 4 which will prevent the erroneously actuated detector from automatically returning to its nonconductive state.

In order to locate a faulty detector once it has been activated, the manually operated switch 6 is opened but current will still flow through the relay and the relay will continue to sound the alarm. The detectors can then be successively disconnected until the faulty detector is located. Upon disconnection of the faulty detector, the alarm will immediately terminate. If one normal detector operates in the case of an emergency and another detector operates because of a fault therein, interruption of the battery voltage will render the normal detector nonconducting and upon reapplication of the battery voltage only the faulty detector will again conduct. Then by opening switch 6 the faulty detector can be readily located as described above. If desired, each detector may be provided with an indicating lamp which is illuminated when the detector is activated. With this invention wherein a voltage is continuously applied, after a detector has been activated, the maintenance of such voltage will cause the indicating lamp to remain illuminated and thus should a faulty detector have caused the alarm, it may be more readily located.

While only certain embodiments of the invention have been illustrated and described, it is apparent that alterations, modifications and changes may be made without departing from the true scope and spirit thereof as defined by the appended claims.

What is claimed is 1. An alarm device comprising a pair of conductors, a plurality of detectors having a minimum operating voltage and connected between said conductors, a relay having a coil and at least one set of normally open contacts, a power supply connected in series with said relay coil and to said conductors, and a resistor connected in series with said normally open contacts and between said conductors, said minimum operating voltage being less than the voltage of said power supply and said resistor having a value such that the voltage drop across the resistor when said contacts are closed is at least equal to said minimum operating voltage. 

1. An alarm device comprising a pair of conductors, a plurality of detectors having a minimum operating voltage and connected between said conductors, a relay having a coil and at least one set of normally open contacts, a power supply connected in series with said relay coil and to said conductors, and a resistor connected in series with said normally open contacts and between said conductors, said minimum operating vOltage being less than the voltage of said power supply and said resistor having a value such that the voltage drop across the resistor when said contacts are closed is at least equal to said minimum operating voltage. 